Control of polyphase slip-ring induction motors



E. PELL Filed May 22, 1948 CONTROL OF POLYPHASE SLIP RING INDUCTION MOTORS Aug. 15, 1950 SPEED PLUGGI G DYNAMIC BRAKING zoo...

Patented Aug. 15, 1950 GONTR 0L,QF BQLYPH-ASE SLIP-RING: NDUCT M rons th B t shrr wwt s-i.

Hammer, Inc., Milwaukee,

of Delaware a s); to Qatar- Wisl, a corporation eiaxglieafi M r 22, 19418,. esame. 8: 5-

4 Claims.

This v ntio e ates o contro Q p lr ese harin inauptio m9. 1

M re rar iaflerh the nr h en relates t 9 r of, uch. a meter harms ts s rqnda Sub.- t e to. t e nfire e or capaciti e rea nts nd. t e nvention. i m r s. oth a n w matted 15 new c mbinat on Qfm ans con ol w r ed hr the Pres n nyent oe s ot. o be onf sed. wi h. t at I in le p a in he tor p mar W i e sub ect ng. t m r s on rr t h influ nce o ca cit v acta i w h. 31 .1; 'qentrql uppl men e by a condenser in the, primary circuit, for neither a f fords the motor speed torque.characteristics pro vided f or b t e nr e. t nt o,n-.

p ent n n o as amqn it b e t t O a n ew spe d. orque meter. cha ac eristi s ad n a eous f r a ur t Q ua ran s. atcu r or the eesltlr ai eqt qn dr v n q ad: 7 the Pl g l g uadrant t e drawn Q r aul ng e d quadrant Another Qbi tt is is Provide desirab e speed r e chara teri i s for a i ra i 9f uad n etlQws e d -Qfthe m ter- AHQH J QDJIQQ- it 12 mfq i'i 59% p ed. t 13? hara t s i s wh eh. a cording o d u tment provide for a qui k 19W d n. rom ful R QQ to a slow speed with little variation. in speed for r ation 1 or f r a QW s able. spe d ith a high L ha y d sce din are We ead t a slow s e d throughout a Wide torque range.

Other qhj eots and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates an embodiment'of the invention which will now be descri e -i. su h em t mtnt the in e being susceptible of modificatiorgg hereinafter mentioned and to other modif cations which will be apparent.

In the drawing,

Figure 1 shows. schematically an induction motor with primary and. secondary control means, both adjustable, and

Figs. 2, 3 and i depict various representative speed torque ohtainab-le through the medium or the control depicted.

Referring to Fig. 1, the same shows an induc tion motor M having a primary B and a secondary S. The motor primary P- is connectable to lines L L Lt or a three phase. alternating curr nt up y t ro gh a ui ab do b e Pe res sw tth 1 l centre-th w t o h it h s tain providing for reversal of: phase rotjationto afford motor torque in either direction accordy o que. 9r t r r i tr t ien a all.

2, ts o r u rem ts an c r i me din e polyphase line connections for the Inotor either inelns r QKQlHSiY i vol a eun a anti means. ac ord ng re ui me t Double pole s. ts a d 3. 9 .5% SeI QtiY ror d ir rereisals. oi phase rotation at will, hile double 91 f r t i rql', o a es e din orer et il l e r the, stant a plic tion he o a e 1 a ance throu h h ed um- 2 he a o rahsk orm r i a s util se a for in ieated r the P s t ve dr v n ua rant .1. 2 t plu in quad:

re and. it W 4; b s i l r v h t. th is made oss b e b dost-r f r w tch 2 and. v w le alternat e de er of s t h 3 nd 5. ro des for Voltage PWQR 9 $1 e a i d v n quadrant. The instant application lacks the conn'eoti on of the Anderson control affording onthe first lowering step a small torque hoisting direction at zero speed. The connections controlled by the switches aforementioned appear too obvious to require description thereof. and as vqill be understood these switches inay be, operable either ally or through the medium of electromagnets or the like. 7

The "motor secondary connections which per se are now known include fixed resistors R}, adjusta e s- R2, ad u abl ma ter P2 eaters R and capacitors C C and C Each phase of the secondary circuit includes in series relation one of the resistors 3 one of theresistors Rfi, and one of the reactors R}. the reactors being terminally re e t d at t ifi reet s lec ed oint to a loopbontaining the capacitors C Q and (3? whereby the capacitors are connected across ferent phases of the motor secondary. The adjustable resistors B have their outer tern ihals interconnected, Whereas said resistors have their opposite terminals connected to different phases i h motel se d ry it 3 2 9. a 5} a n 5 9 et Q res stor B an t? e s e a comm n y r ed t id as ei ref ed to as the rallel r sist s i r t ce. e s onda e ne i n 'efe e qesq e i a e re red. or fl xib it efcqetl el but they are subject to modification. Thus for example where resistance adjustment is not necessary the resistors R and R or either, may be omitted. On the other hand, it is possible to dispense with the resistors R retaining resistors R and R These modifications as well as the preferred connections are per se now known, as are also the effects, generally considered, of all such connections.

However, both subjectingthe motor secondary to the influence of capacitive reactance and subjecting the motor primary to the polyphase voltage of the supply source with such voltage unbalanced, not only appears novel but renders obtainable motor characteristics which are highly advantageous and which have been sought heretofore without success. Also as will appear, such advantageous characteristics are obtainable for difierent quadrants, thus affording the novel control a wide field of utility. Such characteristics are depicted in Figs. 2, 3 and 4 to which reference will now be made.

Fig. 2 depicts motor characteristics obtained through adjustment of the parallel resistance (resistors R the tuning of the motor secondary circuit and the voltage unbalance of the motor primary both being fixed. Curve A depicts the speed-torque characteristic of the motor, with infinite parallel resistance, whereas the characteristic at zero value of the parallel resistance is depicted by curve C, and at an intermediate value of said resistance is depicted by curve B. The characteristic depicted by curve A is especially advantageous in control of a draw bench, for with such characteristic the motor through dynamic braking or plugging will quickly slow down from full speed to a suitable slow threading speed, which because of the slope of the speed torque curve in this region will give but little variation in speed for variation in load. Also the characteristic depicted by curve A is very a va ta eous in printing press control in that it provides for a stable low speed and a high breakaway torque. As will be ap arent, the light load speed may be increased with little change in breakaway torque, by reducing the parallel resistance.

Fig. 3 depicts motor characteristics obtained through varying the volta e unbalance of the motor primary, the paral el resista ce an the tuning of the rector secondary circuit both being fixed- Curve A depicts the speed torque characteristic of the motor with infinite parallel resistance and an intermediate degree of primary voltage unbalance, whereas curve B depicts the characteristic with maximum unbalance and curve C with zero unbalance. Thus varying the degree of unbalance results in a shift in speedtorque characteristic essentially parallel to itself and the speed-torque characteristic here depicted is very advantageous in hoist control in that it provides for selection of stable operating speeds in hoisting at light loads or an empty hook or in lowering overhauling loads. Curve B represents the first speed point lowering of a well known A. C. dynamic lowering hoist controller using the slightly different connections of said Anderson patent.

' Fig. & depicts the speed-torque characteristics obtained through variation in tuning of the motor secondary circuit, the parallel resistance and the degree of primary voltage unbalance being fixed. Curve A depicts the speed torque characteristic with infinite parallel resistance and with resonance at 115% slip, while curve B depicts the characteristic at 170% slip. Thus here again,

as also exemplified in Figs. 2 and 3, the motor speed-torque characteristics are particularly useful where stable low speeds are required.

What I claim as new and desire to secure by Letters Patent is:

1. The method of controlling a polyphase induction motor of the slip ring type to obtain desired speed torque characteristics, which comprises subjectin the motor secondary to the combined influence of capacitive and inductivereactance while at the same time supplying to the motor primary polyphase alternating current from a polyphasesupply source in such manner as to effect voltage unbalance of the motor pri mary in utilizing the polyphase voltage of the supply source.

2. The method of controlling a polyphase induction motor of the slip ring type which comprises subjecting the motor secondary to the combined influence of capacitive and inductive reactance while supplying the motor primary with polyphase current from a polyphase source through means to unbalance the polyphase voltage to which the motor primary is subjected by said source and regulating the influence of the capacitive and inductive reactance and the degree of voltage unbalance for motor speed torque characteristics which according to such regulation provide for a quick slowdown from full speed to a slow speed with little variation in speed for variation in load or a low stable speed with a high breakaway torque or restriction of a descending overhauling load to a slow speed throughout a wide torque range.

3. The combination with a polyphase induction motor of the slip ring type, of a polyphase supply source therefor, a circuit for the secondary of said motor comprising capacitive and inductive reactance and polyphase connections between the motor primary and said source comprising means providing for voltage unbalance of the polyphase current supply to said motor primary.

1. The combination with a polyphase induction motor of the slip ring type, of a polyphase supply source therefor, a circuit for the secondaiy of said motor comprising capacitive and inductive reactance and also adjustable parallel resistance, and polyphase connections between the motor primary and said source comprising adjustable means providing a wide range of voltage unbalance of the polyphase current supply to said motor.

ERIC

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,598,192 Seymour et al Aug. 31, 1926 1,759,551 Greenleaf et al. May 20, 1930 1,866,349 Green July 5, 1932 2,420,192 Rathbun May 6, 1947 FOREIGN PATENTS Number Country Date 212,698 Switzerland Mar. 3, 1936 634,825 Germany Sept. 4, 1936 OTHER REFERENCES An A-C Crane Hoist with Reactor Control by Wickerham et al., Westinghouse Engineer for May 1945, pp. 77-81. 

